Method of making an abrasive cut-off disk



Aug. 31, 1965 w. R. PRATT 3,203,774

METHOD OF MAKING AN ABRASIVE CUT-OFF DISK Original Filed May 8, 1959Fig. 4 Fig. 5 Fig.6

United States Patent 3,203,774 METHQD OF MAKING AN ABRASIVE CUT-GET DESKWillard R. Pratt, Rochester, N35,, assignor to Vanguard AbrasiveCorporation, Le Roy, N.Y., a corporation of New York Griginalapplication May 8, 1959, Ser. No. 811,956, now Patent No. 3,t923,710,dated Apr. 11}, 1962. Divided and this application Dec. 1, 1961, Ser.No. 156,243

:laims. (Ci. 51293) This application is a division of application SerialNo. 8i 1,956, filed May 8, 1959, now Patent 3,028,710, granted April 10,1962.

The present invention relates to an abrasive cut-off disk or whee and,more particularly, to such disks of the type formed by a strong,circular sheet metal drive disk or core having a plurality ofcircumferentially spaced arcuate cutting segments secured around itsperiphery. The arcuate cutting segments typically are composed ofdiamond dust or fragments used as an abrasive and held dispersed andembedded in a metallic matrix. The cutting segments frequently aremanufactured by cold pressing or hot pressing the various ingredientsintroduced into a suitable mold in powder form. The segments prepared inthis manner or any other suitable manner are secured to the periphery ofthe metal drive core by silver soldering or are brazed on. Occasionallyit is desirable in a segment containing diamond dust to isolate thebrazed joint attaching the base of the segment to the drive core fromthe diamond bearing section of the segment. For this purpose, a cuttingsegment of this type sometimes is composed of an outermost diamondbearing section and an inner section of a diamond free material commonlyknown as a backing.

Abrasive cut-off disks of the kind described are used for instance incutting hard non-metallic materials such as concrete, marble, tile, andthe like. Of course, it is desirable to design the cutting segments sothat their cumulative effect produces a superior cutting action whilehaving a longer life than is the case with the other outoff disks ofthis type.

An object of the invention is to provide a new and improved method ofmaking an abrasive cut-off disk of the kind having a metallic drive coreto the periphery of which are secured at circumferentially spaced pointsa plurality of arcuate cutting segments made of an abrasive material.

Another object is the provision of a generally improved and moresatisfactory method of making an abrasive disk of the kind describeddesigned so as to have an improved cutting action and longer life ascompared with other abrasive disks of this type.

Yet another object is to provide a simple and effective method of makingan arcuate cutting segment for attachment to a metallic drive corehaving a section composed of diamond fragments embedded in a metallicmatrix in anarrangement such that the segment has a good performance anda long useful life.

A further object is the provision of a method or process which resultsin a better backing section in a cutting segment of the type having anouter diamond bearing section and a backing of diamond-free material,resulting in a longer life for the segment.

These and other desirable objects may be attained in the mannerdisclosed as an illustrative embodiment of the invention in thefollowing description and in the accompanying drawings forming a partthereof, in which:

FIG. 1 is a fragmentary face view of a cut-off disk to the periphery ofwhich are secured arcuate diamondbearing cutting segments according tothe invention;

FIG. 2 is a fragmentary radial cross-section of the cut-off disk of FIG.1 taken approximately on the line 2-2 thereof;

FIG. 3 is an enlarged side elevational view of the cutting segment shownin FIGS. 1 and 2 according to a first embodiment of the invention;

FIG. 4 is a cross-sectional view to an enlarged scale of the segment ofFIG. 3.

FIGS. 5 and 6 are views similar to FIG. 4 of cutting segments accordingto a second and third embodiment, respectively, of the invention.

The same reference numerals throughout the several views indicate thesame parts.

In FIG. 1 is illustrated an abrasive cut-off disk or wheel constructedin accordance wit-h the invention. The cutotf wheel includes a centralsheet metal drive disk or core .11 made of a suitable wrought metal suchas steel and provided with a central aperture 13 for mounting the diskon a rotating shaft. Secured around the periphery of the core 11 are aplurality of circumferentially spaced arcuate cutting segments 15preferably silver soldered or brazed in an appropriate manner to theouter edge of the core. Desirably the outer edge portions of the core 11are divided into a plurality of equal circumferential segments by anumber of radially extending slots 17. The core 11 is a strong circularsheet metal disk having, as better seen in FIG. 2, a lesser thicknessthan that of the arcuate segments 15 secured to the periphery thereof,which are approximately inch to 4 inch in thickness.

Each of the cutting segments 15 is rectangular in cross section andarcuate when viewed from the face as is more evident in the enlargedview of FIG. 3. The inner radius of the base 19 of each segment 15 issubstantially the same as the outer radius of the core 11, the outerarcuate edge 21 of the segment being approximately concentric with theinner radius. The segment 15 is of the type having diamond dust orfragments used as an abrasive and held dispersed and embedded in asuitable metallic matrix. in the cutting segment illustrated, thediamond dust is embedded only in the outer arcuate section 2.3 of thesegment, the inner arcuate section 25 being free of diamond dust. Theinner portion 25 is commonly known as a backing, and the purpose of thisbacking will be made evident in the discussion to follow.

It has been shown in the use of abrasive cut-off wheels that a superiorcutting action is obtained when the wheel is made to Wear preferentiallyin the center so that the outer edge 21 of the wheel bearing on the workis concave with respect to the surface being cut. This is illustrated inFIG. 4 for a disk which has been in service for a short while. To securedifferential wearing so that this concave edge surface results, thecontent of the abrading material provided by the diamond dust in theouter diamond-bearing section 23 is increased on each side in relationto the content in the center, in the nature of a sandwich arrangement.Thus the two outer side layers 27 and 29 in the diamond-bearing section23 have a greater diamond content than that of the central portion orlayer 31.

As has been mentioned, the diamond dust or fragments in the section 23are held dispersed and embedded in a metallic matrix. Any suitablematrix may be used in carrying out the invention, the common metallicmatrices for this type of cutting segment being bronze, nickel, cupronickel, various iron alloys, and tungsten carbide.

The cutting segment shown in FIGS. 1-4 is provided with the mentionedbacking or inner section 25 which is free of diamond dust. This backingis made of the same metal as provides the matrix in the section 23 andtherefore is also known as a blank. The purpose of this backing is thaton occasion it is desirable to isolate the silver solder or brazed jointattaching the segment 15 to Patented Aug. 31, 1965 t the core 11 fromthe diamond bearing section of the segment in order to secure a betterjoint and improved performance. It is entirely possible, though, toutilize for certain purposes a cutting segment of the kind illustratedin FIG. wherein the backing has been omitted. This cutting segment 33 iscomposed of a sandwich type of diamond-bearing layers identical to thatdescribed for the section 23 in the embodiment of FIG. 4. The layers 27and 29' are identical to the layers 27 and 29 and have the same diamondcontent embedded in an identical metallic matrix, and the central layer31' is identical to the layer 31 and has a correspondingly lower diamondcontent.

The cutting segments of FIGS. 4 and 5 may be manufactured in a number ofways. As one example, a segment of the desired dimensions may be coldpressed by introducing into a suitable mold a powder mixture of thematrix metal and diamond dust in varying proportions. Of course, tomanufacture the segment with the backing as in FIG. 4, an additionalquantity of blank matrix metal is also introduced. The first layerplaced in the mold may have, for example, a diamond content of 36 to 72carats per cubic inch of final volume. The second or center layer mayhave a diamond content of 9 to 18 carats per cubic inch, and a finallayer equal to the first in diamond content with 36 to 72 carats percubic inch. The first and final layers, which become the two sides ofthe segment, may then be compressed to a final dimension of 64, inch toinch and t 16 center layer to 7 inch to 1 inch. These dimensions, ofcourse, are for a particular example and are not intended to belimiting. The sandwich pressed in the manner may then be sintered byclassical and well known methods. Alternatively, the same result may beaccomplished by cold pressing the layers as indicated and thensubsequently hot pressing the compacted mass. A suitable graphite hotpressing die which may be utilized is described in applicants copendingpatent application filed April 22, 1959, Serial No. 808,195, now Patent3,069,816, granted December 25, 1962.

Instead of cold pressing the original compact sandwich layers, therequisite amount of matrix metal and diamond dust for the various layersmay be sintered or fritted loose in a carbon mold to form a slug orpreform that may readily be handled and inserted in a cold press or hotpress mold. These discrete layers may then be fused or compressedtogether by the application of heat and pressure or alternatively ofpressure and a subsequent application of heat.

The times, temperatures, and pressures used in the pressing operationare the conventional times, pressures, and temperatures well known inthe art.

A cutting segment or 33 manufactured in the described manner has asuperior cutting action when its outer edge bearing on the work wearspreferentially in the center to a concave shape. The improved cuttingaction is obtained by the better effect of the edges of the segmentinitially starting the cut rather than the center section or layer. Acutting disk and segment of longer life is obtained by the eliminationof the high pressure on the central section of the segment and thesubsequent fast breakdown clue to pressure.

The blank metal backing section 25 provided inwardly of thediamondbearing section 23 in the embodiment of PEG. 4 is advantageousfor some uses. It has the disadvantage, though, that this type ofbacking is sometimes badly worn by the swarf or cuttings as the wheelturns during operation. Instead of making the backing of matrix metal asexplained, it is possible to make the backing of matrix metal containinga hard wear resistant material such as tungsten carbide, aluminum oxideor the like, but this kind of backing may protrude sutficiently as thecutting segment is worn to cause binding or seizing of the wheel in thecut. To avoid this effect, a cutting segment as shown in FIG. 6employing a layered or sandwich arrangement in the backing section isprovided.

In FIG. 6, the diamond-bearing outer section 23' is identical to thesection 23 previously described and is composed of as before of twoouter layers of relatively high diamond content dispersed and embeddedin a suitable metallic matrix and a central layer of lower diamondcontent in the metallic matrix. A backing section 35 is located, ofcourse, inwardly of the section 23' and is integral therewith. For thisembodiment, a layered struc ture is manufactured having two outer layers37 and 39 of blank matrix metal between which is disposed a centrallayer 41 of abrasive resistant material. The abrasive resistant materialmay be matrix metal containing tungsten carbide, aluminum oxide, or thelike.

In the operation of a cut-oil disk having cutting segments according toFIG. 6, the outer layers 37 and 39 are worn away after a period of useand subsequent wearing of the backing is materially retarded in thecentral section 41 of abrasion resisting material. The reduced size ofthe backing substantially prevents seizing or binding of the wheel inthe cut as the cutting segment edge wears down. As a result, the segmenthas a good performance over a lon er period of use. The segmentaccording to FIG. 6 may be manufactured in a manner similar to thatdescribed for the segments of the other embodiments.

It is seen from the foregoing disclosure that the above mentionedobjects of the invention are well fulfilled. It is to be understood thatthe foregoing disclosure is given by way of illustrative example only,rather than by way of limitation, and that without departing from theinvention, the details may be varied within the scope of the appendedclaims.

What is claimed is:

1. The method of making an abrasive element having greater wearresistance at its lateral edges than in its central portion, whichcomprises the steps of mixing a first batch of powdered matrix metalwith a sufficient quantity of diamond particles to provide a relativelyhigh concentration of diamond particles in the mixture of the firstbatch, mixing a second batch of powdered matrix metal with a relativelylesser quantity of diamond particles to provide a substantially lesserconcentration of diamond particles in the mixture of the second batch,placing a layer of the mixture of the second batch between two layers ofthe mixture of the first batch in sandwich fashion, and compacting thethree layers under heat accompanied by pressure applied approximatelyperpendicular to the lines separating the layers from each other, toform from the three layers an integrally united abrasive element havinga lower concentration of diamond particles and lower wear resistance inits central layer as compared with the diamond particle concentrationand ,wear resistance of its outer layers.

2. The method of making an abrasive cut-off disk having a peripheralcutting face with greater wear resistance at its lateral edges than atits center, which comprises the steps of providing a steel core having aperiphery, providing a series of abrasive elements each made accordingto the method of claim 1, and affixing said abrasive elements to saidcore at spaced intervals around the periphery thereof by solder or thelike.

3. The method of making a diamond bearing abrasive cut-off disk having aperipheral cutting face with greater wear resistance at its lateraledges than at its center, which comprises the steps of providing a sheetmetal core having a periphery at least portions of which are arcuatewith respect to a common center, mixing a first batch of powdered matrixmetal with a sufiicient quantity of diamond particles to provide arelatively high concentration of diamond particles in the mixture of thefirst batch, mixing a second batch of powdered matrix metal with arelatively lesser quantity of diamond particles to provide a substantially lesser concentration of diamond particles in the mixture of thesecond batch, placing an arcuate layer of the mixture of the secondbatch between two arcuate layers of the mixture of the first batch insandwich fashion, compacting the three layers by pressure and fusingthem by heat to form an integrally united abrasive element having aninner arcuate face of concave curvature, an outer arcuate face of convexcurvature substantially concentric with said inner arcuate face, and twolateral faces so substantially plane shape, at least the radiallyoutermost portions of said plane faces and the laterally outermostportions of said convex face being formed from material from said firstbatch and the central portion of said convex face being formed frommaterial from said second batch, repeating the element forming steps toproduce a plurality of such abrasive elements, and afiixing saidabrasive elements to said sheet metal core at intervals around thearcuate portions of the periphery thereof.

4. The method of making a diamond bearing abrasive cut-off disk having aperipheral cutting face with greater wear resistance at its lateraledges than at its center, which comprises the steps of providing a sheetmetal core having a periphery at least portions of which are arcuatewith respect to a common center, mixing a first batch of powdered matrixmetal with a sufficient quantity of diamond particles to provide arelatively high concentration of diamond particles in the mixture of thefirst batch, mixing a second batch of powdered matrix metal with arelatively lesser quantity of diamond particles to provide asubstantially lesser concentration of diamond particles in the mixtureof the second batch, placing an arcuate layer of the mixture of thesecond batch between two arcuate layers of the mixture of the firstbatch in sandwich fashion and placing a quantity of powdereddiamond-free matrix metal in position to make contact with one edge ofall three of said layers, compacting the powdered metal by pressure andfusing it by heat to form an abrasive element having an inner concaveface of diamond free metal, two lateral plane faces of metal from saidfirst batch, and an outer convex face the central portion of which is ofmetal from said second batch and the laterally outer portions of whichare of metal from said first batch, repeating the element forming stepsto provide a plurality of such elements, and aflixing such elements tosaid sheet metal core at intervals around the arcuate portions of theperiphery thereof, with the diamond free concave faces of the elementsnext to the periphery of the core.

5. The method of making a diamond bearing abrasive cut-off disk having aperipheral cutting face with greater Wear resistance at its lateraledges than at its center, which comprises the steps of providing a sheetmetal core having a periphery, providing a first supply of powderedmatrix material containing a relatively high concentration of diamondparticles, providing a second supply of powdered matrix materialcontaining a substantially lesser concentration of diamond particles,providing a third supply of powdered matrix material containingsubstantially no diamond particles, placing a quantity of matrixmaterial from each of said three supplies in position to form anabrasive element having an inner face, an outer face of convex arcuateshape, and two substantially plane lateral faces, arranging thequantities of powdered matrix material in such locations that the innerface of the abrasive element will be formed mainly of material from saidthird supply, the central portion of the outer arcuate face of theelement will be formed mainly of material from said second supply, andthe two lateral edges of the outer arcuate face will be formed mainly ofmaterial from said first supply, applying heat to the quantities ofmatrix material to bond them securely together to make a rigid abrasiveelement, and bonding the abrasive element to a portion of the peripheryof the sheet metal core with said inner face of the element facedinwardly toward the center of the core.

References Cited by the Examiner UNITED STATES PATENTS 2,268,599 1/42Kinney et a1. 51206 2,877,105 3/59 Smith 51-308 3,049,843 8/62Christensen 51206 ALEXANDER H. BRODMERKEL, Primary Examiner.

MORRIS LIEBMAN, Examiner.

1. THE METHOD OF MAKING AN ABRASIVE ELEMENT HAVING GREATER WEARRESISTANCE AT ITS LATERAL EDGES THAN IN ITS CENTRAL PORTION, WHICHCOMPRISES THE STEPS OF MIXING A FIRST BATCH OF POWDERED MATRIX METALWITH A SUFFICIENT QUANTITY OF DIAMOND PARTICLES TO PROVIDE A RELATIVELYHIGH CONCENTRATION OF DIAMOND PARTICLES IN THE MIXTURE OF THE FIRSTBATCH, MIXING A SECOND BATCH OF POWDERED MATRIX METAL WITH A RELATIVELYLESSER QUANTITY OF DIAMOND PARTICLES TO PROVIDE A SUBSTANTIALLY LESSERCONCENTRATION OF DIAMOND PARTICLES IN THE MIXTURE OF THE SECOND BATCH,PLACING A LAYER OF THE MIXTURE OF THE SECOND BATCH BETWEEN TWO LAYERS OFTHE MIXTURE OF THE FIRST BATCH IN SANDWICH FASHION, AND COMPACTING THETHREE LAYERS UNDER HEAT ACCOMPANIED BY PRESSURE APPLIED APPROXIMATELYPERPENDICULAR TO THE LINES SEPARATING THE LAYERS FROM EACH OTHER, TOFORM FROM THE THREE LAYERS AN INTEGRALLY UNITED ABRASIVE ELEMENT HAVINGA LOWER CONCENTRATION OF DIAMOND PARTICLES AND LOWER WEAR RESISTANCE INITS CENTRAL LAYER AS COMPARED WITH THE DIAMOND PARTICLE CONCENTRATIONAND WEAR RESISTANCE OF ITS OUTER LAYERS.